ODOR CONTROL: Something Wicked this Way Comes

Michael Fickes

Phew, P.U., ugh, ick, smelly, stinky. Funny words to most people, but fighting words to those in the solid waste industry.

For solid waste facility managers working in material recycling facilities (MRF), transfer stations and composting plants, odor causes trouble. Smelly plants make neighbors fume and budgets wretch.

Odor control plans, especially those laid on top of existing plants, often do not work as promised or even as well as necessary, leading to ever more odorous complaints and more choking costs.

After the neighbors complained about the odor from a leaf and yard waste facility in Howard County, Md., for example, the operator, Maryland Environmental Services (MES), installed an odor masking spray.

"Our neighbors continued to complain, and eventually we had to shut the plant down," says William Chicca, MES' director of program development and engineering support.

MES also operates a number of MRFs and transfer stations in Maryland. "We don't have too many problems at our MRFs," Chicca says.

"Sometimes in the summer, we have to be careful about restaurant wastes, particularly crab wastes, coming into our transfer stations," he says.

"We move the material through these facilities quickly to avoid problems. In fact, our permit restrictions require that we move all of our wastes out every day. We cannot store anything overnight. This is common throughout Maryland."

Two yard waste facilities operated by MES have reported no problems, thanks to locations remote from residential and commercial developments.

But even the most carefully-planned locations cannot always forestall problems.

E. L. Harvey & Sons Inc. operates a 22,000-square-foot transfer station in Westboro, Mass. According to owner Steve Harvey, the facility operated without problems for years, thanks to a location far away from other developments.

"We had no waste restrictions," he says. "We could take anything that people wanted to send through."

The station produced some odors, especially on hot summer days, but the remote location prevented the odor from becoming a business problem.

Then, a developer bought the adjoining land and erected townhouses. During the summer of 1997, odor from the transfer station wafted above the plant and drifted away. Soon, complaints drifted back.

"When the plans for the development were first made public, we realized we might have a problem and began planning to handle it," Harvey says.

That fall, Harvey installed a spray odor control system manufactured by Nutech Environmental Corp., Denver. "The system uses chemicals to neutralize odors instead of masking them," Harvey explains. "We chose our system by asking for two bids and deciding purely on the cost of the neutralizing chemical.

"We can mix the chemical in concentrations of 500 to one," he continues. "With [such] lower concentration chemicals, it is practical and economical for us to run the system constantly during the summer when the problem comes up."

In addition to the odor control system, Harvey also has decided to divert particularly smelly wastes to an incinerator or to a landfill.

While Harvey has yet to use the odor control system - this year will be the first summer since the installation - he says he is confident that the neutralizing chemicals along with the diversion strategy will satisfy his new neighbors.

The Stench that Ate Brooklyn What do you do about odor at a transfer station in the heart of a major metropolitan area? Waste Management (WMI) of New York, Brooklyn, faced this problem when the neighbors complained about odors emanating from a huge transfer station in Brooklyn.

Permitted to handle 5,000 tons per day, the facility averages about 3,500 tons on most days. WMI also mines incoming waste for recyclables - a process that manages to divert about 20 percent of the incoming waste stream.

In addition to diversion, however, the mining process stirs up the waste and contributes to the facility's odor problem. About two years ago, the stench began to bother the community.

WMI has solved the problem by taking steps in three areas: facility design, process control and odor control.

"We made several design changes in our facility," says spokesperson Susan Clark. "First, we installed roll-down doors leading from the tipping area, the recycling area and the bale-loading area. All of these doors remain shut when there is no traffic in or out.

"Second, at a particularly busy door that cannot be opened and closed constantly, [we] installed a curtain of three-inch wide plastic strips," she continues. "The hanging strips cover about half of the opening. This helps to contain odors as they rise, while allowing the trucks to move in and out without having to wait for the door to open."

WMI also imposed requirements on certain customers. "One of our greatest challenges relates to odors from food wastes coming from fish markets," she says. "We try to control those odors at the source by providing customers with a spray-on odor neutralizer manufactured by FireFreeze [Rockaway, N.J.].

"Customers spray the material into their containers before we pick it up. The cost is factored into their fees. The idea works great."

Last but not least, the facility installed an odor counter-acting system which neutralizes odors manufactured by AiReactor, Maspeth, N.Y.

The system uses a high-pressure atomization process to dispense an odor counteractant mixed with water through tiny nozzles into the air.

The mist evaporates, and the neutralizing chemical fills the air throughout the facility. When it encounters odor molecules, an "ion exchange" occurs and the chemical reaction neutralizes the odor.

"To control odor, you have to create a shield around a building so that odors cannot get out through any opening," says AiReactor's Ralph Landano. "[You] can do this with nozzle assemblies strategically placed near exhaust fans on the roof, over a compactor on the floor, where odors start and where they can get out of a building."

Currently, Landano is working with a firm on the design of a 80,000-square-foot transfer station. For the facility's design, he is recommending a minimum of overhead doors and lots of exhaust fans to move odors out instead of letting them build up inside.

The odor control dispensers will sit near the doors and exhaust vents. "When the doors open, the system will operate," he says. "When the doors close, the system will shut down. The same is true with the exhaust fans."

Bedminster Battles the Big Stink Whichever way the wind blows, large-scale compost processing facilities face the most severe odor problems and consequences.

Over the past few years, a number of major compost plant failures have been attributed to odor in Miami, Portland, Ore., and in Wilmington, Del.

Bedminster Bioconversion Corp., Marietta, Ga., encountered a major odor problem at its Cobb County plant as well. The problem did not cause the plant to fail, but the solution eventually added several million dollars to the plant's original $23 million price tag.

The company has developed a proprietary co-composting technology, which it licenses to other composters and which it uses to design, build and operate facilities under contract for municipalities around the country.

Bedminster has been developing and refining this technology since constructing its first plant in Texas in the early '70s. That plant continues to operate today. Since then, the company has developed plants in Arizona, Florida, Georgia, Massachusetts and Tennessee.

At the Cobb County facility just outside of Atlanta, odor problems accompanied the plant's start up. Residents of homes about 300 feet away noticed the odors and complained.

"We had put in a bio filter using a media mix that included crushed limestone," says Bob Spencer, a Bedminster plant manager. "The limestone clogged the filter, and we could not push air out of the building through the filter system. As a result, the air began to seep out through the doors."

Still in a start-up mode, Bedminster decided to shut down and repair the problem immediately. While shut down, an accumulation of methane gas was ignited by an undetermined source (a lightning strike is suspected) causing a fire in the ceiling panels above the composting floor.

The fire produced about $12 million in damage, a cost largely covered by insurance.

In rebuilding the plant, Bedminster spent about $1 million to redesign, which included work on the odor control system. In that effort, engineers considered odor control from the point of view of facility design, process design and odor neutralization systems. The result is a state-of-the-art system for odor control.

"We aimed for 100 percent air capture in the facility design so that we would have no untreated fugitive emissions to deal with," Spencer says.

When new sludge arrives at the redesigned and rebuilt plant, it is dumped into the sludge pit. Immediately, a hood system drops down over the pit to contain odors. The sludge no longer moves from the pit to the digesters on conveyor belts. Instead, it is enclosed in a pumping system and piped to the digesters.

"We also have installed hoods and air collection systems over the trommel screens and conveyors that process the digested materials," Spencer says.

All of these techniques are called "point source odor control" and aim to capture odor where and when it is produced.

Interestingly, the point source control system has produced some efficiencies in the redesigned plant. Some of the captured air is routed through the system that blows air into the piles, according to Spencer.

"In effect, we're using the most odorous air to aerate the compost piles," he says. "That speeds the composting process and also degrades the strength of the odors."

Another facility design technique draws fresh air into the building through specially-designed louvers. By changing the air in the building in this way, it dilutes the concentration of odor in the air inside the building.

To keep the building buttoned up, Bedminster installed high-speed rolling doors which open and close in about a minute. Above each of the main doors in the facility, an air curtain blasting from top to bottom maintains the seal while the door is opening or closing.

Process design also limits odor production in the plant. "Throughout processing, we maintain airflow through the digesters and piles," Spencer says. "This helps to maintain a positive aerobic state around the material and helps to limit odor production.

"Maintaining a positive aerobic state requires proper design and maintenance of the grates above the trenches to prevent clogging," he continues. "It also requires blower systems to push air through the digesters. Here again, we have installed a point source odor capture system so the bad air doesn't blow out into the room."

In addition, an aeration system pushes fresh air through the material underneath the trommel screens.

Still another process technique involves controlling the mix of materials flowing through the system.

"You have to make sure you have the right recipe for composting," Spencer says. "If you have too much moisture, for instance, you can lose porosity and that will generate foul odors."

Before any air from the plant returns to the outside atmosphere, it flows out of the plant and into water-adsorber scrubbers, which dissolve compounds that contain odor.

The scrubbers send the air into soil-based bio filters containing bacteria and fungi. The bio filters maintain a precise environment that allows these microbes to flourish.

A healthy population of microbes will literally eat the odor molecules flowing into the system. "Bio filtration is very effective," says Spencer. "The odor removal range is 94 percent."

Mmmm. Ah. Fresh air. Comforting words to solid waste managers fighting a war with smell.